Stepping motor

Abstract

A single phase stepping motor has a stator, and a rotor disposed to surround the stator. The stator includes first and second annular stator yokes, which are disposed opposite to each other and have a plurality of pole teeth formed along a circumference thereof, and an annular stator coil disposed between the first and second stator yokes. The rotor includes a ring magnet, which is disposed to surround the first and second stator yokes, and has a plurality of magnetic poles formed along a circumference of the rotor, and a shaft disposed at a center position of the magnet. At least a partial region of a gap formed between each of the pole teeth and the opposing magnetic pole of the magnet is non-uniform in a predetermined direction.

1. A single phase stepping motor comprising:
 a stator; and 
 a rotor disposed to surround the stator, 
 wherein the stator includes: 
 first and second annular stator yokes, which are disposed opposite to each other and have a plurality of pole teeth formed along a circumference thereof; and 
 an annular stator coil disposed between the first and second stator yokes, wherein the rotor includes: 
 a ring magnet, which is disposed to surround the first and second stator yokes, and has a plurality of magnetic poles formed along a circumference of the rotor; and 
 a shaft disposed at a center position of the ring magnet, 
 wherein the pole teeth and the ring magnet are positioned such that a gap is formed between each of the pole teeth and the opposing magnetic pole of the ring magnet, and 
 wherein each of the gaps has a first half side from a center position in a width dimension of each of the pole teeth that is uniform and a second half side that is non-uniform in a predetermined direction. 
 
     
     
       2. The stepping motor according to  claim 1 , wherein the second half side of each of the gaps varies continuously. 
     
     
       3. The stepping motor according to  claim 1 , wherein the gaps are formed so that the center position in the width dimension of each of the plurality of pole teeth is shifted from both a center position of the opposing magnetic pole of the ring magnet and boundary lines for two magnetic poles neighboring to the opposing magnetic pole in a stable position of a detent torque. 
     
     
       4. The stepping motor according to  claim 1 , wherein the rotor rotates in only one direction. 
     
     
       5. The stepping motor according to  claim 1 , wherein each of the gaps is formed so that a stable position of a holding torque does not coincide with a stable position of a detent torque.